Single sheet feed device for an electrophotographic printer or copier

ABSTRACT

Single sheets A are drawn in the usual way from a first stack 8 of single sheets and conveyed on a first recording carrier conveying path 1. At its end there is a switch 10 which alternately feeds the single sheets A to a second and a third recording carrier conveying path 2, 3. In the second recording carrier conveying path 2 which is in the form of a loop, the single sheets A are shifted sideways by the width of one single sheet. A sideways shifted single sheet A1 and a single sheet A2 which has not been shifted sideways simultaneously reach a fourth recording carrier conveying path 4 on which they are conveyed in pairs to a printing unit D which spans the fourth recording carrier conveying path 4 and conveyed out of it again. Subsequently, one single sheet A1 per pair of single sheets is shifted back by the width of one single sheet in a fifth recording carrier conveying path 5 which is also designed as a loop while the other single sheet A2 is conveyed onwards linearly. The single sheets A successively reach in series a second stack 9 of single sheets and are deposited there.

BACKGROUND OF THE INVENTION

The invention relates to a single sheet feed device for anelectrophotographic printer or copier which spans the single sheet feeddevice. In such printers or copiers, exacting requirements are made ofthe printing speed. In printers or copiers according to the prior art aprinting speed of approximately 50 sheets per minute (for example in theDIN A4 format) is achieved. The single sheets are drawn from a singlesheet stack and successively fed by a removal device to a recordingcarrier conveying path of the single sheet feed device. A printing unitwhich contains a developer station and a fixing station is arranged inthe course of the recording carrier conveying path. A print image istransferred to a single sheet in the developer station and in the fixingstation this print image is fixed on the single sheet. In order toensure sufficient quality of the print image, the development and fixingprocess can only be accelerated up to a maximum processing speed. Afurther increase in the processing speed with constant printing qualityis consequently not possible by merely increasing the transfer andfixing speed and thus the conveying speed of the single sheets.

U.S. Pat. No. 4,587,532 discloses a sheet feed device and a sheetdelivery device which are suitable for feeding single sheets to aplurality of printers operating in synchronism. The single sheets arepresent in the form of a stack of single sheets. The sheet feed deviceand the sheet delivery device ensure that a single sheet is fed to eachprinter at the correct time before the subsequent printing cycle beginsand a printed single sheet is conveyed away from said printer. Thelength of the path and the speed of the sheets are selectedappropriately. The feeding speed is higher than the processing speed.However, in order to increase the printing speed a plurality of printingunits arranged one on top of the other is required.

U.S. Pat. No. 4,431,322 discloses a printing device with two recordingcarrier conveying paths which can be selected by means of a switch.Pairs of drive rollers are arranged along the recording carrierconveying paths. These pairs of drive rollers are driven by means ofbelts. Belt speed-transforming transmission means are provided which canbe used to realize different speeds of the pairs of drive rollers. Inorder to increase the printing speed, two printing units are arrangedone on top of the other. Each of the two printing units is assigned arecording carrier conveying path.

U.S. Pat. No. 4,727,402 discloses a single sheet feed device forordering single sheet information carriers in which single sheets can bedrawn off sideways from a stack of single sheets and can be fed to aconveying path in such a way that two single sheets can be conveyedlying one next to the other. The single sheet feed device has aplurality of mechanical and movable individual components, for whichreason complex adjustment and frequent maintenance of the single sheetfeed device are to be expected.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of disclosing a singlesheet feed device for an electrophotographic printer or copier which canbe used to increase the number of printed single sheets per time unitwith constant printing quality and which has a low number of mechanicaland movable individual components so that neither complex adjustment norfrequent maintenance of the single sheet feed device is to be expected.

In general terms the present invention is a single sheet feed device foran electrophotographic printer or copier. A first recording carrierconveying path conveys single sheets serially at first speed which ishigher than the processing speed when printing the single sheets. Aswitch, assigned to the first recording carrier conveying path, selects,as a function of the sequence of sheets, at least one subsequent secondor third recording carrier conveying path. The third recording carrierconveying path is arranged as an extension of the first recordingcarrier conveying path. The second recording carrier conveying path isrouted in such a way that a single sheet which passes through thissecond recording carrier conveying path is shifted sideways by at leastthe width of one single sheet. The switch contains a flap which couplesthe first recording carrier conveying path either to the second or tothe third recording carrier conveying path. The dwell times of thesingle sheets in the second and third recording carrier conveying pathsare matched to one another in such a way that the single sheetssimultaneously reach a printing unit which is arranged downstream, spansthe single sheets, conveys at the processing speed and prints the singlesheets.

Advantageous developments of the present invention are as follows.

A first conveying means, which is arranged in the first recordingcarrier conveying path, takes hold of a single sheet and feeds it to theswitch at the first speed. The second recording carrier conveying pathhas at least a third conveying means which conveys the single sheet at asecond speed in such a way that a single sheet which is conveyed in thesecond recording carrier conveying path is always taken hold of by oneof the third conveying means. The dwell times of the single sheets inthe second and third recording carrier conveying paths are matched toone another in such a way that the front edges of the two single sheetsare aligned when a subsequent fourth recording carrier conveying path isreached. A second conveying means which takes hold of both the first andsecond single sheets when the fourth recording carrier conveying path isreached, conveys them at the processing speed. The first, second andthird speeds are twice as high as the processing speed.

In a further embodiment of the present invention the second recordingcarrier conveying path is designed in a loop-like shape.

In another embodiment of the present invention, a fifth and a sixthrecording carrier conveying path are arranged downstream of the fourthrecording carrier conveying path in such a way that the first singlesheet moves into the fifth recording carrier conveying path and thesecond single sheet moves into the sixth recording carrier conveyingpath. The fifth or the sixth recording carrier conveying path is routedin such a way that the first or second single sheet which passes throughthis fifth or sixth recording carrier conveying path at a fifth speed isshifted back sideways by the width of one single sheet, by the distancewhich the first single sheet had been shifted in the second recordingcarrier conveying path. The sixth or fifth recording carrier conveyingpath is routed in such a way that the second or first single sheet whichpasses through this sixth or fifth recording carrier conveying path at asixth speed can be conveyed without sideways shifting. The dwell timesof the single sheets in the fifth and sixth recording carrier conveyingpaths are matched to one another in such a way that the single sheetssuccessively reach a subsequent seventh recording carrier conveyingpath.

By means of the switch and splitting of the first recording carrierconveying path into a second and a third recording carrier conveyingpath, two single sheets successively drawn off from a stack of sheetsare moved into a position in which they can be processed together in oneprinting unit. If the processing speed corresponds to a maximumprocessing speed, the number of printable single sheets per time unitcan thus be doubled with uniform printing quality.

By selecting the speeds such that the first, second and third speeds aretwice as high as the processing speed, it is ensured that there is anequally large distance between a pair of single sheets conveyed one nextto the other in the fourth recording carrier conveying path and thefollowing pair of single sheets as the distance from one single sheet tothe following single sheet in the first recording carrier conveyingpath.

By means of the arrangement of at least a third pair of conveyingrollers in the second recording carrier conveying path so that a singlesheet which is conveyed in the second recording carrier conveying pathis always taken hold of by a pair of conveying rollers it is ensuredthat the second speed at which the single sheet is conveyed in thesecond recording carrier conveying path is constant over the entirelength of the path. In addition, the pairs of conveying rollers alongthe second recording carrier conveying path ensure reliable guidance ofthe single sheet conveyed there.

A loop-like guidance of the second recording carrier conveying pathpermits, under given spatial conditions, the length of the secondrecording carrier transport path to be selected precisely so that at aprescribed second speed the front edges of the two single sheets arealigned when the fourth recording carrier conveying path is reached.

The further embodiment and design of the invention according to which afifth and sixth recording carrier conveying path are assigned downstreamof the fourth recording carrier conveying path in such a way that thefirst single sheet moves into the area of influence of the fifthrecording carrier conveying path and the second single sheet moves intothe area of influence of the sixth recording carrier conveying pathensure that the paired single sheets are lined up one behind the otherin the correct sequence. For this purpose, the fifth or the sixthrecording carrier conveying path is routed in a loop-like way such thatthe first or second single sheet which passes through this recordingcarrier conveying path at the fifth speed is shifted back sideways bythe width of one single sheet, by which distance the first single sheethad been shifted in the second recording carrier conveying path. Forthis purpose, the sixth or fifth recording carrier conveying path isrouted in such a way that the second or first single sheet which passesthrough this recording carrier conveying path at a sixth speed can beconveyed without sideways shifting. By selecting the dwell times ofthese single sheets in the fifth and sixth recording carrier conveyingpath in such a way that the two single sheets successively reach asubsequent seventh recording carrier conveying path, the originaldistance from single sheet to single sheet of the first recordingcarrier conveying path is restored. Successive stacking of the singlesheets in the correct sequence is thus ensured. This is notdisadvantageous in terms of operation for an operator who prepares thestack of single sheets and removes the printed single sheets from theprinter or copier. If forms which are ordered for example in a specificsequence are to be processed in the printer or copier, then this doesnot give rise to any additional work for the operator because of thedesign of the printer or copier according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The inventory,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and which:

FIG. 1 shows a diagrammatic, spatial illustration of a single sheet feeddevice for branching a recording carrier conveying path,

FIG. 2 shows a detail, containing a loop-like switch, of the singlesheet feed device according to FIG. 1 and

FIG. 3 shows a top view of a chronological sequence of single sheetsaccording to FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The single sheet feed device illustrated in FIG. 1 in which a recordingcarrier conveying path is branched contains a first recording carrierconveying path 1 on which single sheets A which are drawn from a firststack 8 of single sheets can be conveyed to a switch 10 arranged at theend of the first recording carrier conveying path 1. The single sheets Aare taken hold of by a first pair W1 of conveying rollers on the firstrecording carrier conveying path 1 and conveyed by friction at a firstspeed V1 (see FIG. 2).

The switch 10 directs an incoming single sheet A either to a secondrecording carrier conveying path 2 which is routed in a loop-like way orto a third recording carrier conveying path 3 which linearly extends thefirst recording carrier conveying path 1. For this purpose, the switch10 contains a flap which can pivot about an axis 12. The axis 12 runstransversely with respect to the direction in which the recordingcarrier is conveyed. The deflection of the flap of the switch 10 into afirst position in which an incoming single sheet A is fed to the secondrecording carrier conveying path 2 and into a second position in whichan incoming single sheet A is fed to the third recording carrierconveying path 3 is carried out by means of a switchover means which isconstructed as a solenoid actuator 11. An electromotive or pneumaticdrive is also suitable as switchover means 11.

When a single sheet A moves into the second recording carrier conveyingpath 2, then this single sheet A is taken hold of by one, of a total oftwo, third pairs W3.1 of conveying rollers. This third pair W3.1 ofconveying rollers conveys the single sheet A by means of friction intothe loop-like arrangement of the second recording carrier conveying path2 at a second speed V2. In general, for precise guidance of the singlesheet A on the second recording carrier conveying path 2 it issufficient to align the axes of rotation of the third pairs W3.1, W3.2of conveying rollers at a right angle with respect to the direction inwhich the recording carriers are conveyed. However if it is desired toalign an edge of the single sheets A along a run up edge provided at thelateral edge of the second recording carrier conveying path 2, the axesof rotation of the third pairs W3.1, W3.2 of conveying rollers are to bepositioned in such a way that the single sheets A are moved slightlytowards the run up edge.

The third pairs W3.1, W3.2 of conveying rollers are arranged along thesecond recording carrier conveying path 2 at such a distance from oneanother that a single sheet A1 which is conveyed in the second recordingcarrier conveying path 2 is always taken hold of by at least one of thethird pairs W3.1, W3.2 of conveying rollers. As a result it is ensuredthat the conveyed single sheet A1 is always guided precisely andconveyed at exactly the second speed V2.

While being conveyed in the second recording carrier conveying path 2,the conveyed single sheet A1 describes the helical line of a screwthread. The pitch of the thread is selected here such that the singlesheet A1 is shifted, after passing through the second recording carrierconveying path 2, by at least one width of a single sheet with respectto the first recording carrier conveying path 1. The diameter of thethread is selected such that the dwell time of the single sheet A1,conveyed at the second speed V2, in the second recording carrierconveying path 2 is so long that the front edge of the single sheet A1conveyed in the second recording carrier conveying path 2 reaches afourth recording carrier conveying path 4, following the second andthird recording carrier conveying paths 2, 3, at the same time as thefront edge of a single sheet A2 conveyed on the third recording carrierconveying path 3.

On the third recording carrier conveying path, in each case a singlesheet A is conveyed which, on the first recording carrier conveying path1, followed a single sheet A which was fed to the second recordingcarrier conveying path 2 by the switch 10. A single sheet A2 which isconveyed on the third recording carrier conveying path 3 is conveyedthere at a third speed V3. Because of the small length of the thirdrecording carrier conveying path 3, according to the exemplaryembodiment a pair of conveying rollers can be dispensed with in thethird recording carrier conveying path 3. However, it is also possibleto introduce a pair of conveying rollers in this third recording carrierconveying path 3 if this should be necessary.

When the fourth recording carrier conveying path 4 is reached, thesingle sheets A1, A2 coming from the second and third recording carrierconveying paths 2, 3 are taken hold of by one of the second pairs W2.1of conveying rollers arranged along the [lacuna] and fed by friction toa printing unit D which spans the fourth recording carrier conveyingpath 4. In the printing unit D, a print image is transferred onto thesingle sheets A in a developer station contained there and fixed in afixing station also contained in the printing unit D. After fixing ofthe print image has taken place, the single sheets A leave the printingunit D again. The single sheets A are fed by friction along the fourthrecording carrier conveying path 4 on which they are taken hold of by afurther second pair W2.2 of conveying rollers to two subsequentrecording carrier conveying paths 5, 6.

The fifth and sixth recording carrier conveying paths 5, 6 which followthe fourth recording carrier conveying path 4 are, like the second andthird recording carrier conveying paths 2, 3, each half as wide as thefourth recording carrier conveying path 4. They are arranged one next tothe other and can thus in each case pick up one of two single sheets Aconveyed one next to the other from the fourth recording carrierconveying path 4. The fifth recording carrier conveying path 5 intowhich those single sheets are moved which have passed through the secondrecording carrier conveying path 2 before the fourth recording carrierconveying path 4 is reached is also routed in a loop-like form, like thesecond recording carrier conveying path 2. The pitch, diameter andlength of this fifth recording carrier conveying path correspond tothose of the second recording carrier conveying path 2. In the fifthrecording carrier conveying path 5, as in the second recording carrierconveying path 2, two pairs W4.1, W4.2 of conveying rollers arearranged. These fourth pairs W4.1, W4.2 of conveying rollers ensure thatthe single sheet A1 conveyed on the fifth recording carrier conveyingpath 5 is guided precisely and that it maintains the desired speed.

The sixth recording carrier conveying path 6 extends linearly one halfof the fourth recording carrier conveying path 4. In the sixth recordingcarrier conveying path 6 a pair of conveying rollers (not illustrated)is arranged which accelerates the single sheet A2 present in the sixthrecording carrier conveying path 6 to a sixth speed V6 and feeds it to asubsequent seventh recording carrier conveying path 7. In the seventhrecording carrier conveying path 7 an incoming single sheet A1, A2 istaken hold of by a fifth pair W5 of conveying rollers and fed to asecond stack 9 of single sheets at the sixth speed V6.

The ends of the fifth and sixth recording carrier conveying paths 5, 6both lie, viewed in the direction in which the recording carriers areconveyed, opposite the start of the seventh recording carrier conveyingpath 7. A single sheet A1 which comes from the fifth recording carrierconveying path 5 is fed obliquely from above to the seventh recordingcarrier conveying path 7 and a single sheet A2 which comes from thesixth recording carrier conveying path 6 is fed linearly to the seventhrecording carrier conveying path 7.

With reference to FIG. 3, the position of a pair of single sheets A1, A2at different times T1 to T6 is presented below. After the single sheetsA1, A2 from the first stack 8 of single sheets have been successivelyfed to the first recording carrier conveying path 1, the first singlesheet A1 is located, at the first time T1.1, in front of the secondsingle sheet A2 which follows the first single sheet A1 at a smalldistance at the same first time T1.2. The single sheets A1, A2 areconveyed at the first speed V1 to the switch 10 in the direction inwhich the recording carriers are conveyed. When the first single sheetA1 arrives at the flap of the switch 10, this flap is pivoted downwardabout the axis 12 in such a way that the first single sheet A1 iscarried via the switch into the second recording carrier conveying path2. There, the first single sheet A1 is successively taken hold of by thethird pairs W3.1, W3.2 of conveying rollers and carried in a helicalline shape to the fourth recording carrier conveying path 4.

After the first single sheet A1 has passed the switch 10, the solenoidactuator 11 pivots the flap of the switch 10 upward about the axis 12.As a result, the second single sheet A2 which follows the first singlesheet A1 does not move onto the second, but rather onto the thirdrecording carrier conveying path 3, Its length is so short that at asecond time T2.1, T2.2 both the first single sheet A1 and the secondsingle sheet A2 reach the fourth recording carrier conveying path 4lying one next to the other with their front edges aligned. In thisrecording carrier conveying path 4, the pair A1, A2 of single sheets aretaken hold of by a second pair W2.1 of conveying rollers and conveyed atthe processing speed V4 into the printing unit D in the direction inwhich the recording carriers are conveyed. A further second pair W2.2 ofconveying rollers which take hold of the pair A1, A2 of single sheetsand convey them onwards at the processing speed V4 on the fourthrecording carrier conveying path 4 in the direction in which therecording carriers are conveyed are arranged downstream of the printingunit D. At the third time T3.1, T3.2, the single sheets A1, A2 arelocated in front of the printing unit D, and at the fourth time T4.1,T4.2 they are located behind it.

If the first, second, third speeds and the processing speeds, V1, V2,V3, V4 were exactly equal, a distance of the length of one single sheetA would arise between the pairs of single sheets A conveyed on thefourth recording carrier conveying path 4. This enlargement of thedistance between the single sheets A1 would reduce the number of singlesheets A which can be printed per time unit. An enlarged distancebetween the single sheets A can however be avoided according to theinvention in that the processing speed V4 is smaller than the first,second and third speeds V1, V2, V3 and in an extreme case is halved.

Starting from the position at the fourth time T4.1, T4.2, the singlesheet A1 reaches the fifth recording carrier conveying path 5 and thesecond single sheet A2 reaches the sixth recording carrier conveyingpath 6. At the fifth time T5.1, T5.2, the single sheets A1, A2 arealready in the aforesaid recording carrier conveying paths 5, 6. Inthese recording carrier conveying paths 5, 6, the single sheets A1, A2are conveyed at a fifth and at a sixth speed V5, V6. The fifth and sixthspeeds V5, V6 are twice as high as the processing speed V4. As a resultthe single sheets A which are fed in in pairs are successively conveyedaway so quickly that there can be no blockage of single sheets.

Since the sixth recording carrier conveying path 6 is substantiallyshorter than the fifth recording carrier conveying path 5 which is ofloop-like design, the second single sheet A2 reaches the seventhrecording carrier conveying path 7 first, and when the single sheet A1arrives it is already conveyed so far that the two single sheets A1, A2do not touch. At the sixth time T6.1, T6.2, both single sheets A1, A2are located completely on the seventh recording carrier conveying path 7and are subsequently successively deposited on the second stack 9 ofsingle sheets.

In the exemplary embodiment described, the sequence of single sheets Awhich are conveyed in pairs is respectively inverted, i.e. a singlesheet A1 which is conveyed in front of a second single sheet A2 in thefirst recording carrier conveying path I is located behind the secondsingle sheet A2 on the seventh recording carrier conveying path 7.However, this is not generally a problem since the single sheets areusually unprinted before passing through the printing unit D. However ifthe stacking sequence such as is present in the first stack 8 of singlesheets has to be reproduced again when stacking sheets into the secondstack 9 of single sheets, all that is necessary is to interchange thefifth and sixth recording carrier conveying paths 5, 6. The stackingsequence has to be maintained for example when printing forms. Insteadof the pairs W of conveying rollers, conveying belts or a tractor drivecan also be used. This has no influence on the subject matter of theinvention.

The invention is not limited to the particular details of the apparatusdepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described apparatuswithout departing from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A single sheet feed device for anelectrophotographic printer or copier for conveying single sheets to andfrom a printing unit having a processing speed for printing the singlesheets, comprising:a first recording carrier conveying path whichconveys the single sheets serially at a first speed which is higher thanthe processing speed of the printing unit when printing the singlesheets; a switch, assigned to the first recording carrier conveyingpath, for selecting, as a function of sequence of sheets, at least oneof subsequent second and third recording carrier conveying paths; thethird recording carrier conveying path being arranged as an extension ofthe first recording carrier conveying path; the second recording carrierconveying path being routed such that a single sheet which passesthrough the second recording carrier conveying path is shifted sidewaysby at least a width of one single sheet; the switch having a flap whichcouples the first recording carrier conveying path either to the secondrecording carrier conveying path or to the third recording carrierconveying path; and dwell times of first and second single sheets in thesecond and third recording carrier conveying paths, respectively, beingmatched to one another such that the first and second single sheetssimultaneously reach the printing unit which is arranged downstream,which spans the first and second single sheets, which conveys the firstand second single sheets at the processing speed and which prints thefirst and second single sheets.
 2. The single sheet feed device asclaimed in claim 1, wherein the single sheet feed device furthercomprises:a first conveying device which is arranged in the firstrecording carrier conveying path and which takes hold of a single sheetand which feeds the single sheet to the switch at the first speed; inthe second recording carrier conveying path at least one third conveyingdevice which conveys a single sheet at a second speed such that thesingle sheet which is conveyed in the second recording carrier conveyingpath is always taken hold of by one of the third conveying devices; thedwell times of the first and second single sheets in the second andthird recording carrier conveying paths, respectively, being matched toone another such that front edges of the first and second single sheetsare aligned when a subsequent fourth recording carrier conveying path isreached; and a second conveying device which takes hold of both thefirst and second single sheets when the fourth recording carrierconveying path is reached and conveys them at the processing speed. 3.The single sheet feed device as claimed in claim 2, wherein in the thirdconveying path single sheets are conveyed at a third speed and whereinthe first, second and third speeds are twice as high as the processingspeed.
 4. The single sheet feed device as claimed in claim 2, whereinthe single sheet feed device further comprises:a fifth recording carrierconveying path and a sixth recording carrier conveying path that arearranged downstream of the fourth recording carrier conveying path suchthat the first single sheet moves into the fifth recording carrierconveying path and the second single sheet moves into the sixthrecording carrier conveying path; one of the fifth and the sixthrecording carrier conveying paths being routed such that one of thefirst and second single sheets, which passes through this recordingcarrier conveying path at a fifth speed, is shifted back sideways by thewidth of one single sheet, and by the distance which the first singlesheet had been shifted in the second recording carrier conveying path;the other of the sixth and fifth recording carrier conveying paths beingrouted such that the other of the second and first single sheets whichpasses through this recording carrier conveying path at a sixth speed isconveyed without sideways shifting; and dwell times of the first andsecond single sheets in the fifth and sixth recording carrier conveyingpaths being matched to one another such that the first and second singlesheets successively reach a subsequent seventh recording carrierconveying path.
 5. The single sheet feed device as claimed in claim 1,wherein the second recording carrier conveying path is designed in aloop-like shape.